The principal object of the present invention is to satisfy a need for a convenient and economical device to enable users to monitor, and thus gain control over, the amount of AC electrical power being consumed by appliances at any given time.
Without such a monitoring means, the user is apt to leave the premises with a number of electrical appliances turned on, which could or should be turned off during the user's absence. A safety or fire hazard can sometimes be created when heavy current-consuming appliances are left unattended.
At the present time, no ready economical means is available for power consumption monitoring without utilizing relatively expensive instrumentation, including means to penetrate or otherwise make contact with the conductors of power supply cable, which is impractical and in some cases illegal.
While certain snap-on meters are known in the prior art which do not require penetration of a cable sheath, these devices are not operable with the multiple (two or three) conductor power supply cables presently in wide use.
The essence of the present invention therefore resides in the provision of a non-penetrating, externally applied sensing unit particularly constructed to coact with AC power supply cables, by electromagnetic induction, or as a Hall effect sensor. An AC signal from the sensor is converted in a 2 volt AC meter which can be read in kilowatt equivalents.
The device is based on the following principles:
(1) The concentric magnetic field around any conductor is directly proportional to the current flowing in the conductor.
(2) Magnetic fields around parallel supply condudtors are in opposing relationship, thus creating elliptical fields where the major elliptical axes are across the axes of the parallel conductors.
(3) Lines of magnetic flux cutting across a conductor will induce current flow in that conductor. A similar effect can be obtained by the placement of a Hall effect sensor in the flux field generated by a conductor.
An object of the invention is to provide a device of the above-mentioned type for monitoring power consumption in the home or elsewhere which, except for the sensor, can be constructed from commercially available economical components, thus enabling the manufacturing and sale of the device at relatively low cost.
Another object is to provide a device of the mentioned typed which is entirely practical and reliable.
Other objects and advantages of the invention will become apparent during the course of the following detailed description.